Support is planned OpenCL 1.0 in Cycles?
Not all ATI cards are supported. 

The list of supported cards per Blender Development can be found here. While this is not the entire list of cards that have shown to work, I believe they are the GPUs that have been tested "working" by development. From what I've observed from other ATI users, any card that does not have OpenCL 1.2 or 2.0 support, does not work with Blender 2.75 (and 2.74 w/ ATI Patch), and will not show in the list of Computing Devices.

With that said, Blender only works with the latest drivers from AMD, and if that driver does not have the OpenCL support for older cards, Blender will not support it. On a good note, the Blender viewport will support more versions of OpenGL in the future. Some users have had luck using beta drivers with older cards, and using an ATI patched Blender (2.74.5 - 2.75rc2).